The present invention relates to signal measurement techniques, and more particularly to a method of frequency response measurement of sinusoidal test signals of various frequencies.
It is of interest to use an automated method of measuring the amplitude of sinusoidal test signals of various frequencies of analog and digital signals, such as video signals. Examples include packet or burst amplitudes of a “multi-burst” test signal, such as shown in FIG. 1, or the amplitude of a swept sinusoid signal at a particular frequency. Prior methods of measuring such signals either measure the peak, envelope, curve fitting or other derivative aspect of the amplitude of the multi-bursts. The prior methods for swept sinusoids generally use Fourier Transforms (FT), such as fast Fourier Transforms (FFT), discrete Fourier Transforms (DFT), etc. The peak methods are the most susceptible to errors due to noise and non-linear distortions. The envelope detection methods are less susceptible to noise, but are not robust in the presence of non-linear distortions. The FT methods are useful for relative amplitude measurements of a linear sweep, but do not allow a direct measurement of absolute amplitude for a portion of a sweep or multi-burst at a particular frequency. Also even FT methods optimized for speed, such as FFTs, are relatively computationally expensive if only one or a few frequencies are of interest.
It is desired to have one method of frequency measurement that is robust in the presence of random noise, quantization error, MPEG impairments and other non-linear distortions and interference. Also desired is a method of determining a figure of merit correlated to the probable accuracy of the frequency measurement due to impairments, such as those from MPEG and/or noise. Further it is desired that the frequency measurement work with sinusoidal test signal components, such as bursts, with various time windows—duration and envelope shape, burst spacing, etc.—and with a swept sinusoid. Finally it is desired that the method works with different video standards, such as YPbPr, RGB, high definition, standard definition and computer video, and with variable sample rates not necessarily known a priori or related to a clock rate of the corresponding digitized video.